Bulletproof coffee is said to increase metabolism in the body and brain

Bulletproof coffee, which has high-profile fans in Hollywood, Silicon Valley and in the sporting world, is one of the latest beverage trends to catch on here.

Popular with health nuts, it is simply black coffee with a knob of unsalted butter - similar to the kopi gu you (butter coffee) we have here - laced with a special ingredient: medium-chain triglyceride (MCT) oil.

Served in a handful of cafes and eateries here, bulletproof coffee is said to increase metabolism both in the body and the brain, thanks to the MCT oils.

Found in largest quantities in coconut oil - up to 60 per cent - MCTs can also be found in palm kernel oil, breast milk, cow and goat milk, said Dr Daniel Wai, an endocrinologist in private practice.

These fat molecules can also be found in the form of powders and oils here, like the dr. MCT range of products developed by local company Keto Science.

Unlike normal fat molecules, MCTs do not get repackaged into fat particles, then stored away in the body.

Ms Zhang, who is in private practice, said: "They are best used for beverages, dressings, desserts, sauces and off-heat cooking.

"In other words, add it in as a final ingredient after heat is turned off."

But as with all things, these fat molecules should be taken in moderation.

Taking too much of these oils can cause stomach discomfort and diarrhoea, said Dr Wai.

He suggested starting with small amounts of MCTs, then gradually increasing the amount.

Dr Wai added: "Overconsuming MCT oils - close to 100 per cent of fat intake - is not desirable as we still need other saturated and unsaturated fats like Omega-3 and Omega-6, as well as fat-soluble vitamins.

"MCTs should not constitute more than 40 per cent of your total fat intake."